The main objective of the proposed research is: (1) to enhance the understanding of the role of the gastrointestinal hormones in the regulation of colonic smooth muscle activity and (2) to determine the cellular mechanism through which the hormones act. Myoelectrical activity will be measured and correlated with contractile activity in cat colonic smooth muscle using extracellular glass pore electrodes and a force displacement transducer in vitro. The efficacy of the agonist hormones, gastrin and cholecystokinin, and the antagonist hormone, secretin, will be determined through the analysis of Michaelis - Menten transformation of the dose response curves. Antagonists of the autonomic nervous system will be used to determine if the gastrointestinal hormones act directly on smooth muscle or through neural receptors. A double sucrose gap will be used to evaluate the mechanism of action of the gastrointestinal hormones at the cellular level. Estimates of membrane conductance and ionic current flows following application of the hormones can be measured by this technique.